DENVER (AP) — Police have arrested a boy in a shooting that critically injured a teenage boy outside of a Denver middle school.

Police said Wednesday that the suspect is being held for investigation of aggravated assault.

The shooting happened near Cole Middle School northeast of downtown on Tuesday afternoon. Police haven't said what led up to it.

The charter middle school serves grades six through eight and is part of Denver Public Schools' STEM program.

Classes are in session with heightened security Wednesday.